Ernst Mayr

What Evolution Is

The conclusion that these favored individuals had been selected to survive requires an answer to the question, Who does the selecting? In the case of artificial selection, it is indeed the animal or plant breeder who selects certain superior individuals to serve as the breeding stock of the next generation. But, strictly speaking, there is no such agent involved in natural selection. What Darwin called natural selection is actually a process of elimination. The progenitors of the next generation are those individuals among their parents' offspring who survived owing to luck or the possession of characteristics that made them particularly well adapted for the prevailing environmental conditions. All their siblings were eliminated by the process of natural selection.

Herbert Spencer, when saying that natural selection is nothing but 'the survival of the fittest,' was indeed quite right. Natural selection is a process of elimination, and Darwin adopted Spencer's metaphor in his later work. However, his opponents claimed that it was a tautology, a circular statement, by defining 'the fittest' as those who survive, but this is a misleading claim. Actually, survival is not a property of an organism but only an indication of the existence of certain survival-favoring attributes. To be fit means to possess certain properties that increase the probability of survival.